The conventional vehicle is provided with a transmission system between the internal combustion engine and the driving wheels. The conventional transmission system varies the driving force and wheel speed in accordance with widely variable driving conditions of the vehicle itself to allow the engine to fully develop its own performance. There are a variety of continuously variable transmission systems like those which are disclosed in official publications of Japanese Patent Laid-Open Nos. 57-186656 (1982), 59-43249 (1984), 59-77159 (1984), and 61-233256 (1986) for example. Any of these conventional continuously variable transmission systems transmits the driving force by either expanding or contracting the radius of belt rotation by either expanding or contracting the width of the belt channel formed between a stationary pulley member secured to the revolving shaft and a movable pulley member mounted axially movably to the revolving shaft so that it can come into contact with and leave the stationary pulley shaft for varying the belt drive ratio.
Any conventional continuously variable transmission system is subject to feedback control against an objective value set by applying either the number of the engine revolution or the belt drive ratio determined by the throttle aperture while controlling the transmission system. As a result, any conventional transmission system executes control over the transmission against the objective value independent of the shift position. This in turn prevents the conventional transmission control system from freely choosing a variety of transmission characteristics from the standpoint of economical driving performance, sporty performance, and engine-brake effect, and at the same time the driving characteristic required by the driver cannot be satisfactorily achieved.
An object of the invention is to overcome those disadvantages mentioned above by providing a novel method of controlling a continuously variable transmission system by executing sequential steps including the following: delivering a throttle-aperture detection signal and a vehicle-speed detection signal to a controller unit; determining an optimum objective number of engine revolution in reference to a first objective number of engine revolution set by the throttle-aperture detection signal and a second-objective number of engine revolution set by the vehicle-speed detection signal and in accordance with the instruction limiting the number of engine revolution at the shift position; and executing control of the transmission system in response to the vehicle-speed detection signal. This allows the continuously variable transmission control system of the invention to achieve a satisfactory driving characteristic matching the vehicle-speed detection signal and varies responsiveness when setting the objective number of engine revolution, thus eventually providing a satisfactory driving characteristic matching the requirement of the driver.
To achieve the above object, the system for controlling a continuously variable transmission related to the invention controls the transmission by either expanding or contracting the width of belt channel between a stationary pulley member and a movable pulley member which is axially removably mounted relative to the stationary pulley member to either expand or contract the radius of rotation of the belt wound on the cooperating pair of pulleys for varying the belt drive ratio, in which the control method is comprised of the sequential steps including the following: delivery of a throttle-aperture detection signal and a vehicle-speed detection signal to a controller unit; and determination of an optimum objective number of engine revolution in reference to a first objective number of engine revolution set by the throttle-aperture detection signal and a second objective number of engine revolution set by the vehicle-speed detection signal and, in accordance with the instruction, limiting the number of engine revolution at the shift position to eventually control the transmission system in accordance with the established optimum objective number.
By virtue of the invention, while the vehicle is driven, the continuously variable transmission control system delivers the throttle-aperture detection signal, the vehicle-speed detection signal, and the instruction for limiting the number of engine revolution at the shift position to the controller unit to determine the optimum objective number of engine revolution for executing control of the transmission system. By applying the vehicle-speed detection signal, a specific transmission characteristic can be generated in accordance with the shift position and switches, and at the same time, control responsiveness can be varied by setting the objective number of the engine revolution, thus making it possible for the system to satisfy the driving characteristic required by the driver.